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Publication numberUS20040097034 A1
Publication typeApplication
Application numberUS 10/613,203
Publication date20 May 2004
Filing date3 Jul 2003
Priority date7 Jun 2000
Also published asUS6617206, US8421140, US20060258113
Publication number10613203, 613203, US 2004/0097034 A1, US 2004/097034 A1, US 20040097034 A1, US 20040097034A1, US 2004097034 A1, US 2004097034A1, US-A1-20040097034, US-A1-2004097034, US2004/0097034A1, US2004/097034A1, US20040097034 A1, US20040097034A1, US2004097034 A1, US2004097034A1
InventorsGurtej Sandhu, Guy Blalock
Original AssigneeSandhu Gurtej S., Blalock Guy T.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Capacitor structure
US 20040097034 A1
Abstract
A capacitor structure and method of forming it are described. In particular, a high-K dielectric oxide is provided as the capacitor dielectric. The high-K dielectric is deposited in a series of thin layers and oxidized in a series of oxidation steps, as opposed to a depositing a single thick layer. Further, at least one of the oxidation steps is less aggressive than the oxidation environment or environments that would be used to deposit the single thick layer. This allows greater control over oxidizing the dielectric and other components beyond the dielectric.
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Claims(59)
What is claimed is:
1. A substrate assembly, comprising:
a support surface; and
a plurality of high-K dielectric layers over said support surface, wherein a common metal is present in at least two adjacent layers of said plurality.
2. The substrate assembly in claim 1, wherein said plurality of high-K dielectric layers comprises a first high-K dielectric layer contacting said support surface.
3. The substrate assembly in claim 1, further comprising a barrier layer between said support surface and said plurality of high-K dielectric layers.
4. The substrate assembly in claim 1, wherein said support surface is a capacitor electrode.
5. The substrate assembly in claim 1, wherein said plurality of high-K dielectric layers defines a thickness of at most 200 Angstroms.
6. The substrate assembly in claim 5, wherein said plurality of high-K dielectric layers comprises a first high-K dielectric layer contacting said support surface and defining a thickness of at least a monolayer.
7. The substrate assembly in claim 6, wherein said first high-K dielectric layer defines a thickness of at least 10 Angstroms.
8. A capacitor dielectric, comprising:
a first high-K capacitor dielectric comprising a metallic element; and
a second high-K capacitor dielectric comprising said metallic element and contacting said first high-K capacitor dielectric.
9. The capacitor dielectric in claim 8, wherein said first high-K capacitor dielectric defines a first thickness; and wherein said second high-K capacitor dielectric defines a second thickness that is different from said first thickness.
10. The capacitor dielectric in claim 8, wherein said first high-K capacitor dielectric and said second high-K capacitor dielectric are oxides.
11. The capacitor dielectric in claim 10, wherein said first high-K capacitor dielectric is a first oxide; and wherein said second high-K capacitor dielectric is a second oxide different from said first oxide.
12. The capacitor dielectric in claim 10, wherein said first high-K capacitor dielectric contains a first amount of oxygen; and wherein said second high-K capacitor dielectric contains a second amount of oxygen different from said first amount.
13. A capacitor structure, comprising:
a first electrode layer;
a dielectric layer disposed over said first electrode layer, wherein said dielectric layer comprises a plurality of consecutively-positioned sub-layers, wherein each of said sub-layers comprises a high-dielectric-constant material, and wherein said dielectric layer comprises oxygen and an additional element common to all sub-layers of said plurality; and
a second electrode layer disposed over said dielectric layer.
14. A method of insulating a semiconductor device, comprising:
providing a series of insulating layers for said semiconductor device under oxidizing conditions; and
controlling oxidation beyond said series of insulating layers by way of said oxidizing conditions.
15. The method in claim 14, wherein said step of providing a series of insulating layers comprises providing a series of insulating layers defining a total thickness; and wherein said step of controlling oxidation comprises ensuring that a cumulative effect on oxidation from providing said series of insulating layers is less than an effect of oxidizing one insulating layer defining said total thickness.
16. The method in claim 15, wherein said step of providing a series of insulating layers comprises providing a series of oxide layers.
17. The method in claim 16, wherein said step of providing a series of oxide layers comprises providing a series of high-K oxide layers.
18. A method of depositing a high-K dielectric onto a surface, comprising:
providing a first layer of said high-K dielectric over said surface using a first group of oxidation parameters that generally insufficient to oxidize said surface; and
providing a second layer of said high-K dielectric over said first layer using a second group of oxidation parameters that generally insufficient to oxidize said surface.
19. The method in claim 18, further comprising a step of depositing a barrier layer onto said surface; and wherein said step of providing a first layer of said high-K dielectric comprises depositing said first layer onto said barrier layer, wherein said first group of oxidation parameters allow oxidation of said barrier layer and are generally insufficient to oxidize said surface.
20. The method in claim 18, wherein said step of providing a first layer comprises:
depositing a material; and
subsequently oxidizing said material using said first group of oxidation parameters.
21. The method in claim 18, wherein said step of providing a first layer comprises depositing a material using said first group of oxidation parameters.
22. The method in claim 18, further comprising a step of reoxidizing a selection of said first layer and said second layer using a third group of oxidation parameters that are generally insufficient to oxidize said surface.
23. A method of providing insulation, comprising:
providing a substrate configured to receive a high-K dielectric material having a thickness and resulting from a first set of oxidizing parameters and only one deposition step; and
depositing said thickness of said high-K dielectric material onto said substrate in a plurality of deposition steps using at least a second set of oxidizing parameters that allow less oxidation than said first set.
24. The method in claim 23, wherein said step of depositing said thickness of said high-K dielectric material comprises additionally using said first set of oxidizing parameters.
25. The method in claim 23, wherein said step of depositing said thickness of said high-K dielectric material comprises additionally using a third set of oxidizing parameters that allow more oxidation than said first set.
26. A method of processing a capacitor electrode configured to oxidize in response to providing an amount of high-K oxide for said electrode using a first set of oxidizing conditions including a process time, an ambient temperature, an ambient pressure, an ambient atmosphere, and excitation source values; wherein said method comprises:
providing a first portion of said amount of high-K oxide for said electrode using a second set of oxidizing conditions that are less aggressive than said first set; and
providing a second portion of said amount of high-K oxide.
27. The method in claim 26, wherein said step of providing a second portion comprises providing said second portion at a temperature differing from a temperature included as part of said second set of oxidizing conditions.
28. The method in claim 26, wherein said step of providing a second portion comprises providing a second portion in an ambient atmosphere differing from an ambient atmosphere included as part of said second set of oxidizing conditions.
29. The method in claim 26, wherein said step of providing a second portion comprises providing a second portion differing in depth from said first portion.
30. A method of forming a capacitor structure for a substrate assembly, comprising:
forming a first electrode layer on said substrate assembly;
forming a first capacitor dielectric layer portion over said first electrode layer, said first capacitor dielectric layer portion comprising a metal element;
forming a second capacitor dielectric layer portion over said first capacitor dielectric layer portion, said second capacitor dielectric layer portion comprising said metal element, wherein said first capacitor dielectric layer portion and said second capacitor dielectric layer portion in combination provide at least a portion of a total capacitor dielectric layer, and wherein said total capacitor dielectric layer exhibits a dielectric constant greater than ten; and
forming a second electrode layer over said total capacitor dielectric layer.
31. The method of claim 30, wherein said total capacitor dielectric layer exhibits a dielectric constant greater than twenty.
32. The method of claim 30, wherein said total capacitor dielectric layer comprises a dielectric material selected from a group consisting of: perovskites, ferroelectrics, high-dielectric-constant oxides, doped versions of each of said preceding materials, and combinations thereof.
33. The method of claim 32, wherein said step of forming a first electrode layer comprises forming said first electrode layer using a first conductive material selected from a group consisting of: doped silicon, platinum, palladium, rhodium, gold, iridium, silver, titanium nitride, tin nitride, ruthenium nitride, zirconium nitride, ruthenium dioxide, tin oxide, titanium monoxide, and combinations thereof.
34. The method of claim 33, wherein said step of forming a second electrode layer comprises forming said second electrode layer using a second conductive material selected from a group consisting of: copper, platinum, palladium, rhodium, gold, iridium, silver, titanium nitride, tin nitride, ruthenium nitride, zirconium nitride, ruthenium dioxide, tin oxide, titanium monoxide, titanium silicide, aluminum, and combinations thereof.
35. The method of claim 30, wherein said total capacitor dielectric layer comprises a dielectric material selected from a group consisting of: (Ba,Sr,Pb,La)(Ti,Zr)O3, bismuth titanate, potassium tantalate, lead niobate, lead zinc niobate, potassium niobate, lead magnesium niobate, tantalum pentoxide, and combinations thereof.
36. The method of claim 35, wherein at least a portion of said total capacitor dielectric layer is doped with a dopant material selected from a group consisting of: Na, Al, Mn, Ca, La, Nb, F, K, Cr, Mn, Co, Ni, Cu, Zn, Li, Mg, Cl, V, Mo, Ce, Pr, Nd, Sn, Eu, Gd, Th, Dy, Ho, Er, Ta, W, and combinations thereof.
37. A method of allowing capacitance to be generated, comprising:
providing a plurality of high-K dielectric layers for a capacitor, said plurality representing a continuous sequence of materials sharing a common non-oxygen component; and
providing an oxidizing environment for said plurality of high-K dielectric layers.
38. The method in claim 37, wherein said step of providing a plurality of high-K dielectric layers comprises depositing a plurality of oxide layers; and wherein said step of providing an oxidizing environment comprises providing said oxidizing environment during said step of depositing a plurality of oxide layers.
39. The method in claim 37, wherein said step of providing a plurality of high-K dielectric layers comprises depositing a plurality of non-oxide layers; and wherein said step of providing an oxidizing environment comprises providing an oxidizing environment after depositing each non-oxide layer of said plurality of non-oxide layers.
40. The method in claim 37, wherein said step of providing a plurality of high-K dielectric layers comprises depositing a plurality of oxide layers; and wherein said step of providing an oxidizing environment comprises providing an oxidizing environment after depositing all of said plurality of oxide layers.
41. The method in claim 37, wherein said step of providing an oxidizing environment comprises providing a rapid thermal oxidation environment.
42. The method in claim 37, wherein said step of providing an oxidizing environment comprises providing a furnace oxidation environment.
43. The method in claim 37, wherein said step of providing an oxidizing environment comprises providing a plasma oxidation environment.
44. The method in claim 37, wherein said step of providing an oxidizing environment comprises providing an anodic oxidation environment.
45. A method of providing a capacitor dielectric defining a total thickness, comprising:
depositing an initial layer of a high-K capacitor dielectric, said initial layer defining an initial thickness that is less than said total thickness; and
depositing an additional amount of said high-K capacitor dielectric onto said initial layer, said additional amount defining an additional thickness, wherein said initial thickness plus said additional thickness equal said total thickness.
46. The method in claim 45, wherein said step of depositing an initial layer comprises depositing an initial layer defining an initial thickness ranging from 10% to 40% of said total thickness.
47. The method in claim 45, wherein said step of depositing an initial layer comprises depositing an initial layer defining an initial thickness ranging from about 14% to 80% of said total thickness.
48. A method of depositing multiple layers of a high-K capacitor dielectric on a workpiece in a furnace, comprising:
establishing deposition parameters within said furnace, comprising:
introducing a tantalum precursor into said furnace at a rate ranging from 10 sccm to 2000 sccm,
introducing an oxygen-containing gas into said furnace at a rate ranging from 0.1 SLM to 5 SLM,
establishing a pressure inside said furnace ranging from 0.1 Torr to 10 Torr, and
establishing a temperature inside said furnace ranging from 400 C. to less than 800 C.;
exposing said workpiece to said deposition parameters for less than 30 minutes;
allowing a first tantalum-based layer to form on said workpiece in response to said exposing step; and
depositing a second tantalum-based layer directly onto said first tantalum-based layer.
49. The method in claim 48, wherein said step of establishing a temperature inside said furnace comprises establishing a temperature inside said furnace of around 450 C.
50. The method in claim 48, wherein said step of exposing said workpiece to said deposition parameters comprises exposing said workpiece to said deposition parameters for about one minute.
51. The method in claim 48, wherein:
said step of introducing a tantalum precursor comprises introducing tantalum chloride; and
said step of introducing an oxygen-containing gas comprises introducing N2O.
52. A capacitor dielectric, comprising a plurality of capacitor dielectric layers defining a total thickness ranging from 50 to 70 angstroms, wherein each layer of said plurality is a high-K dielectric defining an individual thickness ranging from 10 to 40 angstroms in thickness, and wherein each layer of said plurality comprises a metal oxide included within an adjacent layer of said plurality.
53. The capacitor dielectric of claim 52, wherein at least a lowest layer of said plurality defines an individual thickness of about 20 angstroms.
54. A method of providing a BST dielectric, comprising:
forming an initial BST layer at a temperature of less than 650 C. for a time sufficient to define a layer ranging from 20 to 80 Angstroms thick; and
forming a subsequent BST layer over said initial BST layer.
55. The method in claim 54, wherein said step of forming an initial BST layer comprises forming an initial BST layer at a temperature of at least 400 C.
56. The method in claim 55, wherein said step of forming a subsequent BST layer comprises forming a subsequent BST layer onto said initial BST layer.
57. A method of forming an amount of Ta2O5 over a metal electrode, comprising:
providing a first portion of Ta2O5 over said metal electrode at a temperature of less than 500 C., wherein said first portion is less than said amount; and
providing an additional portion of Ta2O5 onto said first portion at a temperature ranging from 400 C. to 700 C.
58. The method in claim 57, wherein said step of providing a first portion of Ta2O5 comprises providing a first portion having a first thickness; and wherein said step of providing an additional portion of Ta2O5 comprises providing an additional portion having a second thickness different from said first thickness.
59. A metal-insulator-silicon device, comprising:
a top metal electrode;
a top Ta2O5 layer under said top metal electrode;
a bottom Ta2O5 layer under said top Ta2O5 layer and contacting said top Ta2O5 layer;
a silicon nitride layer under said bottom Ta2O5 layer; and
a bottom silicon electrode under said silicon nitride layer.
Description
    FIELD OF THE INVENTION
  • [0001]
    The present invention relates generally to a capacitor structure and its method of manufacture. More particularly, the present invention relates to a capacitor structure for high-density memory arrays.
  • BACKGROUND OF THE INVENTION
  • [0002]
    Without limiting the scope of the invention, its background is described in connection with prior methods of forming capacitor structures for dynamic random access memory (DRAM) using high-dielectric-constant materials (or high-K dielectrics). By high-dielectric-constant, it is meant a dielectric constant greater than 10 at room temperature, and preferably a dielectric constant greater than 20.
  • [0003]
    Advances in miniaturization of integrated circuits have led to smaller areas available for devices such as transistors and capacitors. For example, in semiconductor manufacture of a memory array for a DRAM, each memory cell comprises a capacitor and a transistor. In a conventional DRAM, pairs of memory cells are located within regions (“memory cell areas”) defined by intersecting row lines (“word lines”) and column lines (“bit lines” or “digit lines”). Accordingly, to increase memory cell density of the memory array, row lines and column lines are positioned with minimal spacing (“pitch”). Using minimal pitch in turn constrains memory cell area. In high-density memory array architecture, a memory array will have a bit line-to-bit line pitch equal to or less than 0.5 microns.
  • [0004]
    In conflict with reducing memory cell area is maintaining a sufficient amount of memory cell charge storage capacitance. Each DRAM memory comprises a capacitor for storing charge. A capacitor is two conductors separated by a dielectric, and its capacitance, C, is mathematically determinable as:
  • C=(εrε0 A)/d,
  • [0005]
    where εo is a physical constant; dielectric constant, εr, is a material dependant property; distance, d, is distance between conductors; and area, A, is common surface area of the two conductors.
  • [0006]
    To increase capacitance, C, per unit area, the DRAM industry is pursuing depositing materials with a high permittivity for use as capacitor dielectrics. Many perovskites, ferroelectrics, and other high-dielectric-constant materials have capacitance densities greater than standard silicon dioxide (SiO2) and silicon nitride (Si3N4) capacitor dielectrics.
  • [0007]
    Many perovskites have the chemical formula ABO3, where A is one or more monovalent, divalent, or trivalent elements and B is one or more pentavalent, tetravalent, trivalent, or divalent elements. Examples of high-dielectric-constant ferroelectric oxides include niobium pentoxide (Nb2O5); tantalum pentoxide (Ta2O5); and titanates including lead zirconate titanate (PbTiZrO3, abbreviated PZT) and barium strontium titanate (BaSrTiO3, abbreviated BST). Other high-dielectric-constant materials include but are not limited to non-oxide ferroelectrics, such as barium fluoride (BaF2) and magnesium fluoride (MgF2). Depending on the dielectric constant, εr, of these materials, as well as the application, they may be used in parallel plate capacitor structures, such as stack capacitors or mini-stack capacitors, or vertical capacitor structures including container capacitors and trench capacitors.
  • [0008]
    High-dielectric-constant oxides are conventionally deposited in one step at elevated temperatures (greater than 500 degrees Celsius) in an oxygenated atmosphere (such as O2). Examples of processes for depositing high-dielectric-constant oxides are ionbeam sputtering, chemical vapor deposition, and pulsed laser deposition. It has been found that in such an environment, the capacitor electrode layer oxidizes, thereby causing an unwanted reduction in capacitance. Moreover, such high-dielectric-constant oxides are often annealed or re-oxidized after deposition, which further exacerbates the oxidation problem.
  • [0009]
    In addition, other problems may occur if high-dielectric-constant oxide dielectrics are deposited directly on silicon (Si) capacitor electrodes. In addition to oxidation or other undesirable reactions between the electrode and dielectric, silicon may migrate into the high-dielectric-constant oxide, thereby reducing its permittivity and the capacitor's capacitance.
  • [0010]
    One option to at least partially prevent these problems is to provide a barrier layer, such as a layer of germanium (Ge) or silicon nitride (Si3N4), between the silicon electrode and the high-dielectric-constant oxide. The oxidation conditions present after the deposition of this barrier layer may result in the oxidation of that layer, but this is actually preferable in certain circumstances. Regardless, it is desired in the art that this layer will prevent oxidation of the electrode. Unfortunately, the oxidation conditions in effect while forming the entirety of the high-K dielectric in one step often still cause oxidation of the silicon electrode despite the presence of the barrier layer. In addition, forming a barrier layer adds complexity to the manufacturing process and reduces the effective dielectric constant of the capacitor.
  • [0011]
    As an alternative to depositing dielectric on a silicon electrode, high-dielectric-constant oxides may be deposited on nonreactive metals or conductive metal oxides comprising the capacitor electrode. The term “nonreactive” when used in context with contact to a high-dielectric-constant oxide herein means a material that provides a stable conductive interface during and after processing. Examples of nonreactive metals include noble metals such as lead (Pd) or platinum (Pt). Exemplary conductive metal oxides include ruthenium oxide (RuO2). Single and multiple metal layers may used to form the capacitor electrode. However, while this solves some of the problems associated with silicon electrodes, the problem of oxidizing the electrode during or after the formation of the high-K dielectric still exists.
  • [0012]
    As a result, it would be desirable to form a high-dielectric-constant oxide such that the likelihood of decreasing capacitance is reduced.
  • SUMMARY OF THE INVENTION
  • [0013]
    Accordingly, the present invention provides a dielectric for a capacitor structure or other device, and method of formation thereof. Rather that provide a single layer of dielectric under a particular set of oxidation parameters, one exemplary embodiment of the current invention instead provides a plurality of thinner dielectric layers, wherein providing at least the layer nearest the capacitor electrode is accomplished under less aggressive oxidizing parameters. Such exemplary embodiments allow for greater control over the oxidation that may occur beyond the dielectric.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • [0014]
    Features and advantages of the present invention will become more apparent from the following description of the preferred embodiments described below in detail with reference to the accompanying drawings where:
  • [0015]
    [0015]FIGS. 1A and 1B are cross-sectional views of in-process DRAM substrate assemblies of the prior art.
  • [0016]
    [0016]FIGS. 2A and 2B are cross-sectional views of exemplary embodiments in accordance with the present invention.
  • [0017]
    [0017]FIGS. 3A and 3B are cross-sectional views of exemplary embodiments in accordance with the present invention having undergone additional processing.
  • [0018]
    Reference numbers refer to the same or equivalent parts of embodiments of the present invention throughout the several figures of the drawing.
  • DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • [0019]
    In the following detailed Description of the Preferred Embodiments section, reference is made to the accompanying drawings which form a part of this disclosure, and which, by way of illustration, are provided for facilitating understanding of the exemplary embodiments. It is to be understood that embodiments other than the exemplary embodiments disclosed herein may be practiced without departing from the scope of the present invention. The following exemplary embodiments, directed to manufacture of dynamic random access memories (DRAMs), are provided to facilitate understanding of the present invention. Accordingly, some conventional details with respect to manufacture of DRAMs have been omitted to more clearly describe the exemplary embodiments herein.
  • [0020]
    Referring to FIG. 1A, there is shown a cross-sectional view of an in-process DRAM substrate assembly 10 of the prior art. By substrate assembly, it is meant a substrate comprising one or more layers formed thereon or therein. Further, in the current application, the term “substrate” or “semiconductor substrate” will be understood to mean any construction comprising semiconductor material, including but not limited to bulk semiconductive materials such as a semiconductor wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). Further, the term “substrate” also refers to any supporting structure including, but not limited to, the semiconductive substrates described above. Substrate assembly 10 comprises a slice of a single crystalline semiconductor 11. In semiconductor 11, a well 12 is formed. In well 12 are formed conductive implant regions 14. Shallow trench isolation regions 13 are formed in semiconductor 11 by removing a portion thereof and filling the remaining hole with one or more dielectric materials. Transistor gate stacks 16 are formed on semiconductor 11, and are separated from conductive studs 15 by spacers 17. Dielectric layers 18 and 19 are deposited and etched to provide holes for deposition of conductive layer 20.
  • [0021]
    Conductive layer 20 is then polished to form a planar surface. As chemical-mechanical-polishing (CMP) is conventionally used for such polishing, photosensitive polymer 21 is deposited to protect substrate assembly 10 from potential contaminants associated with CMP. Conductive layer 20 provides bottom electrodes for container capacitor structures.
  • [0022]
    Dashed-lines 5 indicate a proximate location for a contact via for connection to a conductive stud 15 therebelow. Separation 7 between dashed-lines 5 and outer surface 9 of conductive layer 20 bottom electrodes is about or less than 0.1 microns for a high-density DRAM array.
  • [0023]
    Notably, though an exemplary embodiment of the present invention is described herein in terms of a container capacitor structure for a high-density DRAM array, it should be understood that the present invention may be employed to form container, stack, mini-stack, trench, or other capacitor structures in DRAM devices or in devices other than DRAM. The present invention may be implemented in a variety of other integrated circuit devices including but not limited to memory devices, logic devices having embedded memory, application specific integrated circuits, microprocessors, microcontrollers, digital signal processors, and the like incorporating a memory array which employs one or more capacitors. Moreover, a memory or a memory module having a capacitor formed in accordance with the present invention may be employed in various types of information handling systems. Such systems include network cards, telephones, scanners, facsimile machines, routers, televisions, video cassette recorders, copy machines, displays, printers, calculators, and personal computers, and the like systems incorporating memory.
  • [0024]
    Again, referring to FIG. 1A, conductive layer 20 provides a first electrode for a capacitor structure; in the exemplary embodiment illustratively shown, it is a container capacitor structure; however, conductive layer 20 may be thought of as a bottom electrode for any form of capacitor. Conductive layer 20 may be formed of one or more layers of one or more materials. An optional barrier layer 4 may be formed between conductive layer 20 and conductive stud 15 to limit unwanted effects due to diffusion. Examples of oxygen diffusion limiting barrier materials that are conductors include metal nitrides, conductively formed semiconductors (e.g., germanium doped with a material designated as an electron acceptor or an electron donor), and conductively formed semiconductor nitrides (e.g., silicon nitride doped with a material designated as an electron acceptor or an electron donor). This barrier layer 4, however, does not limit or prevent unwanted effects of interaction between conductive layer 20 and a subsequently deposited high-dielectric-constant capacitor dielectric. As a result, another barrier layer 3, such as the one described in the background section and pictured in FIG. 1B, may be provided between these layers.
  • [0025]
    With respect to these examples, oxidation of the conductive layer 20 will occur during or after a one-step formation of the full amount of high-K dielectric that will be used in the completed capacitor. By way of example and not limitation, if conductive layer 20 comprises silicon and a high-dielectric-constant oxide is deposited on it, then silicon dioxide may be formed. In addition, oxygen may reach other layers under the conductive layer 20 and create undesirable effects in other materials. Further, other undesirable reactions or material migrations may also occur.
  • [0026]
    To mitigate unwanted interaction, the present invention offers exemplary embodiments that allow for formation of a high-K dielectric under conditions that minimize if not completely prevent oxidation beyond the dielectric. Rather than form the entire amount of dielectric at once under a given set of parameters, exemplary embodiments teach forming the dielectric in a plurality of steps, wherein each step provides only a portion of the total dielectric to be used in the completed device. Moreover, at least a first oxidation step involved with providing the dielectric is carried out under parameters that result in less aggressive oxidation in comparison to the prior art parameters.
  • [0027]
    Referring to FIG. 2A, there is shown a cross-sectional view of an in-process DRAM substrate assembly 10A in accordance with the present invention. Conductive layer 20 may comprise an acceptor or donor doped semiconductor, platinum, palladium, rhodium, gold, iridium, silver, titanium nitride, tin nitride, ruthenium nitride, zirconium nitride, ruthenium dioxide, tin oxide, titanium monoxide, and combinations thereof. FIG. 2B illustrates an alternative exemplary portion of a substrate assembly 10B, wherein conductive layer 20 comprises hemispherical-grain-silicon having phosphorous added thereto for conductivity. Also added to the substrate assembly 10B is a silicon nitride barrier layer 3.
  • [0028]
    In either embodiment, a first layer 22 of capacitor dielectric 24 is subsequently formed. First layer 22 may be formed at least in part by chemical-vapor-deposition (CVD), physical-vapor-deposition (PVD), jet-vapor deposition (JVD), liquid deposition (e.g., spin-on, liquid injection, and the like), atomic layer deposition/epitaxy (ALD/ALE), or other means for controlled deposition of a material. Further, it should be noted that at least one oxidation step is used in providing many kinds of capacitor dielectric both in prior art and in exemplary embodiments of the current invention. For instance, oxidation may play an integral part of the initial deposition process so that an oxide is formed as a direct result of that process. Directly depositing a tantalum oxide is one example. Alternatively, a non-oxide may be initially deposited, followed by an oxidation step. Depositing tantalum and then oxidizing that layer into tantalum oxide serves as an example of this alternative process. Regardless of the method used to provide the oxide, such an oxide is often later subjected to an anneal in an oxidizing ambient in order to fill oxygen vacancies and burn away impurities in the oxide. Any of these oxidation steps can take place by way of one or a combination of oxidizing methods.
  • [0029]
    Many of these oxidizing methods involve subjecting the substrate assembly 10A/10B to a thermal process in an oxygen containing atmosphere. Such an atmosphere may contain a gas including O2, O3, N2O, NO, H2O, or combinations thereof. The thermal energy can be provided in a furnace, wherein resistance to the conduction of electricity through the furnace coils generates the heat for the substrate assembly 10A/10B. As another option, the substrate assembly 10A/10B could be placed in a rapid thermal process device such as the Centura HT tool, sold by Applied Materials, set to RTO (rapid thermal oxidation) mode. In such a device, a lamp shines light on the substrate assembly 10A/10B, which heats in reaction to absorbing the light. Alternatively, a reactor could be used to generate an oxygen-containing plasma, remote or local, for the substrate assembly 10A/10B. As yet another option, an anodic oxidation process using an electrolytic solution could be used to provide the oxidizing environment.
  • [0030]
    Returning to the tantalum oxide example, prior art indicates that it is known to deposit, in one step, 50 to 70 Angstroms of tantalum oxide. Exemplary parameters for doing so involve a CVD process wherein a tantalum precursor such as tantalum chloride (TaCls) is carried by a gas such as argon into a furnace at a rate of 10 sccm to 2000 sccm. Further, an oxygen-containing gas such as N2O is introduced to the furnace at a rate of 0.1 SLM to 5 SLM. The pressure inside the furnace is at 0.1 Torr to 10 Torr, and the temperature inside the furnace ranges from 800 C. to 850 C. Under parameters such as these, the full amount of tantalum oxide will form after about 30 minutes. In contrast, an exemplary embodiment of the current invention involves providing a first layer 22 of tantalum oxide whose thickness is within the range of 10 to 40 Angstroms (preferably 20 Angstroms), wherein deposition can occur in the same furnace and with the same atmosphere but at a lower temperature—ranging from 400 C. to less than 800 C. (preferably around 450 C.)—and a process time of about 1 minute. Thus, assuming that it is desired to ultimately have a dielectric thickness of 50-70 Angstroms, this exemplary embodiment teaches initially providing about 14% to 80% of that total.
  • [0031]
    As another example, BST can be deposited as the first layer 22. Prior art teaches providing a full 200 Angstroms at 650 C. Embodiments of the current invention allow for initially providing a first layer 22 comprising BST, wherein the thickness ranges from 20-80 Angstroms and the temperature is less than 650 C., preferably between 400 C. and less than 650 C. Assuming that it is desired to ultimately have a dielectric thickness of 200 Angstroms, this exemplary embodiment teaches initially providing about 10% to 40% of that total.
  • [0032]
    As a third example, it is assumed that a Metal-Insulator-Metal (MIM) capacitor configuration is desired, wherein tantalum pentoxide Ta2O5 serves as the insulator. Prior art involves deposition parameters such as an ozone ambient and a temperature of 500 C., wherein the parameters result in the full amount of high-K dielectric being deposited. Exemplary embodiments of the current invention allow for less than the full amount of high-K dielectric to be initially deposited under less aggressive oxidation conditions in terms of time, temperature, pressure, oxygen source, other ambient gasses, or any other parameter.
  • [0033]
    These examples demonstrate that the oxidation environment used during or after the deposition of the fill amount of high-K oxide to be used in the capacitor results from a cooperation of several parameters, including the ones specified above as well as others such as the presence of excitation sources (like plasma or UV radiation) and their associated values. The current invention includes within its scope exemplary embodiments wherein less than the full amount of high-K oxide is initially provided, and oxidation associated with that initial amount is less than the oxidation that occurs in relation to depositing the full amount. The oxidation may occur during the deposition of an oxide dielectric, after the deposition of a non-oxide layer, or after the oxide has been provided. The oxidation may occur by way of any known method of oxidation, such as RTO, furnace oxidation, or other methods described above. The lesser oxidation is achieved by altering the oxidation parameters, such as in the ways described above as well as others.
  • [0034]
    After depositing and oxidizing first layer 22, second layer 23 of capacitor dielectric 24 is formed, as illustratively shown in the cross-sectional views of FIGS. 3A and 3B. Second layer 23 can be formed in a manner similar to that of the first layer 22. However, that is not a requirement under the current invention. Second layer 23 may be deposited with different oxidation parameters in effect during or after deposition. Further, it is not necessary that the oxidation parameters for the second layer 23 be less aggressive than those for the first layer 22. Returning to the MIM example, the second layer 23 of Ta2O5 can be deposited at a temperature ranging from 400 C. to 700 C. Thus, the oxidation parameters can exceed even those used in the prior art to oxidize the full amount of high-K dielectric deposited in one step. In addition, second layer 23 may be provided to define a thickness differing from the thickness of the first layer 22. Moreover, the type of high-K dielectric may be different from the high-K dielectric forming the first layer 22 in terms of the types of high-K dielectric components or their proportion.
  • [0035]
    High-dielectric-constant materials that may be used include perovskites, ferroelectrics, high-dielectric-constant oxides, acceptor doped perovskites, acceptor doped ferroelectrics, acceptor doped high-dielectric-constant oxides, donor doped perovskites, donor doped ferroelectrics, donor doped high-dielectric-constant oxides, and combinations thereof. The high-dielectric-constant material may be doped with a material selected from: Na, Al, Mn, Ca, La, Nb, F, K, Cr, Mn, Co, Ni, Cu, Zn, Li, Mg, Cl, V, Mo, Ce, Pr, Nd, Sn, Eu, Gd, Th, Dy, Ho, Er, Ta, W, and combinations thereof.
  • [0036]
    By repetitively forming sub-layers of capacitor dielectric 24, a desired thickness may be achieved while allowing greater control of the oxidation process than one would have by forming one layer of capacitor dielectric having that thickness. In embodiments such as the one depicted in FIG. 3A, oxidation may be generally restricted to the capacitor dielectric 24, thereby leaving the conductive layer 20 substantially free of oxide. A similar result may be achieved in the exemplary embodiment depicted in FIG. 3B, but it would be preferred to allow oxidation to extend to the barrier layer 3 while still leaving the conductive layer 20 substantially free of oxide. The above described methods allow such a result.
  • [0037]
    After forming a plurality of sub-layers of capacitor dielectric 24, conductive layer 25 may be deposited to provide a top electrode portion for capacitor 8. Conductive layer 25 may comprise acceptor doped silicon, donor doped silicon, copper, aluminum, platinum, palladium, rhodium, gold, iridium, silver, titanium nitride, tin nitride, ruthenium nitride, zirconium nitride, ruthenium dioxide, tin oxide, titanium monoxide, and combinations thereof.
  • [0038]
    It should be understood that substrate assembly 10A of FIGS. 2A, 2B, 3A and 3B may be formed in a single chamber 100 or in a cluster of chambers 100 without breaking vacuum. It should be understood that though only two sub-layers 22 and 23 are described herein, the present invention may be employed to provide two or more sub-layers for forming capacitor dielectric layer 24.
  • [0039]
    The present invention has been particularly shown and described with respect to certain preferred embodiments. However, it will be readily appreciated to those of ordinary skill in the art that a wide variety of alternate embodiments, adaptations or variations of the preferred embodiments, and/or equivalent embodiments may be made without departing from the intended scope of the present invention as set forth in the appended claims. For example, the thickness of the initially deposited dielectric sub-layer can be as little as the thickness of one atom comprising that layer (in which case the sub-layer would be considered to be a “monolayer”) depending upon the tendency of subsequent processing steps to encourage oxygen diffusion. Further, it should be understood that exemplary embodiments of the current invention have applications in metal-insulator-silicon (MIS) structures as well as MIM structures discussed above and other structures known in the art. For instance, at least one exemplary embodiment of the current invention allows for an MIS device comprising a top metal electrode, a top Ta2O5 layer under the top metal electrode, a bottom Ta2O5 layer under the top Ta2O5 layer, a silicon nitride layer under the bottom Ta2O5 layer, and a bottom silicon electrode under the silicon nitride layer. In addition, the current invention is not limited to providing a capacitor dielectric. Rather, the invention has applications in any circumstance wherein controlling the oxidation of a dielectric or other insulator layer is beneficial. Accordingly, the present invention is not limited except as by the appended claims.
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Classifications
U.S. Classification438/243, 257/E21.283, 257/301, 257/E27.087, 257/310, 257/309, 257/E21.01, 257/E21.648, 257/E21.019
International ClassificationH01L27/108, H01L29/76, H01L21/316, H01L21/02, H01L21/8242
Cooperative ClassificationH01L28/55, H01L28/56, H01L21/31637, H01L27/11507, H01L27/10811, H01L21/31654, H01L28/91, H01L27/10852, H01L28/65
European ClassificationH01L27/108M4B2, H01L28/56, H01L28/91, H01L27/108F2B, H01L21/316C2
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